I suspect the DirectSound errors are just another example of sound being broken for some people with the current version of Proton. I get the same messages, including the same lack of audio. The weird broken characters are meant to be in Japanese. You should be able to workaround that by setting LC_ALL=ja_JP.utf8, provided you have a Japanese locale installed.
EDIT: Music works with vanilla Wine, albeit an older version (3.0.2). I will test with 3.7 shortly for a more direct comparison, and because more recent versions appear to have a regression, causing the game to crash completely.
EDIT 2: I can confirm the game runs correctly with wine-3.7, including music.
So it's a regression then which means it can probably be fixed. Thanks!
I'll install 3.7 too later today to see what happens.
Could you please try using IndirectSound. It fixed the sound issue in MaxPayne for me.
The sound issue seems to be fixed for me now, with this and other games. There seemed to have been a lot of small updates for my installed games, so perhaps it was fixed there.
@UnspeakableHorror the regression is unrelated to the issues reported here, just a further problem that will need to be taken into account if Proton is updated to a newer Wine version.
@thirdeyefunction I can confirm that Planetarian is now working correctly without issues in windowed mode. Fullscreen still has the weird flicker.
Seems you are correct, one of the updates fixed it.
Nothing extracted yet.
Weird white image:

After transition and font selection:

Sound error:

System